Jumbo25

Simple question but one I can’t find a simple answer to. My wife and I returned to the UK from France on 7th March and I understood we should tell HMRC asap even though we are not tax resident immediately. Using the government gateway says we are too early to register. Do we literally wait 183 days and try again or is there a simpler way? We are trying to avoid being asked for 6 month’s tax in one go.